Hydraulic mortar or cement composition

ABSTRACT

A hydraulic mortar or cement composition which is suitable for application by spray coating and useful in sealing the walls of galleries in coal mines or other excavations, comprises limestone marl containing a small concentration of clay, slightly burnt and completely deacidified cement clinker, and a small amount of an anhydrous calcium salt such as calcium chloride to accelerate initial hardening.

AU 112 EX United States Patent Mikoteit et al.

[ 1 Feb. 29, 1972 Joachim Tennstedt, Enniger, both of Germany [73] Assignee: Elsa Zementand Kalkwerlre Aktiengesellschaft, Neubeckum, Westphalia, Germany [22] Filed: Apr. 17, 1970 [21] Appl. No.: 29,682

[30] Foreign Applimtion Priority Data l Apr. 25, 1969 Germany ..P 19 21 084.5

[52] US. Cl ..l06/89, 106/97 [5 l] lnt. Cl. ..C04b 7/02 [58] Field of Search l06/89, 97

[56] References Cited UNITED STATES PATENTS 2,880,100 3/1959 Ulfstedt ..l06/89 Primary Examiner-James E. Poer Anorney-Bums. Doane, Swecker 8L Mathis [5 7] ABSTRACT aimall amount of an wall such as cLium chloride to accelerate initial hardening.

6 Claims, No Drawings HYDRAULIC MORTAR OR CEMENT COMPOSITION BACKGROUND OF THE INVENTION The present invention relates to a novel hydraulic mortar composition adapted to sealing and waterproofing of the walls and other surfaces of galleries, chamber, bulkheads and the like in mines and other underground excavations.

in underground mining, deposits of coal or ores are reached by driving either vertical, sloping, or horizontal shafts or adits, from which additional tunnels are driven until all the desired parts of the deposit are brought within reach. The two principal methods of underground excavation are stoping and caving. Stoping involves drilling, blasting and cutting of the coal or ore for subsequent removal. in so-called open stoping, coal or ore pillars are left for the purpose of giving support, or else the stope may utilize simple timber supports or props. Filled stopes are employed where chambers, having been fully excavated and depleted of coal or ore, are filled with tailings or waste rock to provide wall support. Caving is the practice of undercutting a block and allowing the weight of coal or ore and the overburden to cave it in and break it up. Mine workings may comprise tunnels, drifts, crosscuts, shafts, stopes and rooms. Coal, particularly bituminous coal, occurs in horizontal beds, and its mining may involve problems with dangerous gases, such as methane or carbon monoxide.

in the room and pillar system of mining coal the rooms are separated by long rectangular pillars which support the main weight of the roof, supplemented by timber props which serve to prevent slabs and pieces of the roof from falling, and if necessary, headboards. The props may be capped by a sill to form a set, which may be rectangular or trapezoidal in fonn. The props or sets are generally placed about 3 meters apart.

Bulkheads are conventionally placed in shafts, stopes or inclines that are being used for working purposes while in process of extension. They consist of heavy timber platforms which are braced from one side. In stoping bulkheads are used to confine filling material, and in this capacity they act as retaining walls.

The prop sets are arranged transversely of the room or chamber wall faces. To protect the completed surfaces of the walls, to prevent spontaneous combustion by vagrant ventilating currents in the old workings, and to eliminate climatic difficulties at the coal face due to ventilation losses in rooms from which the coal has been removed, it is customary to erect wood props additionally, parallel to the wall faces in order to support the roof in the portion of the working area already excavated, the spaces between the props then being filled with tailings or waste rock, and if necessary, further sealed. The wood props are intended to sustain the pressure of the roof strata, and the tailings or waste rock are intended to obviate ventilation losses so as to improve the ventilation in the work ing sections. The wood props are generally erected about 3 meters apart.

However, it is necessary for the wall faces to be frequently relined. Moreover the wood props cannot satisfactorily take up the pressure of the rock, since local stresses arise owing to this nonuniform support of pressure. Moreover the gas seal is inadequate without additional sealing, since the filling material loosely distributed between the props is permeable to gas.

It is conventional practice to pack the cavities between the supported cross-sectional and the unsupported cross-sectional areas of the galleries in underground workings with tailings or waste rock. This allows accumulations of methane to take place in the cavities, and in any event produces unventilated places.

It has long been known to apply a flexible sprayed coating to the concave surfaces and sealing members in periphery of the galleries. Where only slight strengths are necessary, a slurry of cement and stone dust may be used to good effect. However, where greater strengths are required, mixtures of cement and mortar are used for this purpose. Thus, for example, a cementsand mixture, conveyed by a stream of air at high velocity and be coated is commonly used in mining work. The layer deposited in this way is quite dense and impervious to water and can be used to prevent slabbing or flaking off of the rock surfaces where this is caused by the action of air or moisture upon the exposed rock surface. it can also be applied to mine timbers as a fireproofing agent. However, for wallwork this known composition has the disadvantage that there is a limit to the thickness of the layer that can be applied without sloughing off of the layer taking place.

A disadvantage of the hardened mixtures of conventional cement and mortar is their friability, so that the sprayed coat cracks under the slightest pressure. In order to seal ofl' excavated wall faces in underground coal mining, bulkheads may be employed, which are constructed by erecting support walls at the end and the beginning of the bulkheads in'the excavated sections and then filling the cavity formed by the supporting walls with filling material, as indicated previously, which may be applied either by hand or mechanically. Thereafter a pumpable slurry of a virtually pure, high-analysis limestone and, if necessary, cement, and water, may be apjcelerators and rapid setting agents, of conventional types, can

plied. The erection of such a bulkhead is a very expensive operation involving high labor costs.

A cement slurry is also used for strengthening rock and for sealing ofi' seepage water, being injected into the exposed rock by means of a probe located in a sealed borehole. However, the cement slurry is frequently washed out by the seepage water, thereby rendering useless the entire efiort.

GENERAL DESCRIPTION OF THE INVENTION In accordance with the present invention, there is provided a novel hydraulic mortar mix or cement mix which is especially adapted for the coating of the walls, bulkheads, timbers, and other appurtenances of mine working, and which is free from the disadvantages of known mortars employed for these The hydraulic mortar or cement mix of the present invention comprises four active ingredients, as follows:

1. A hydraulic binding agent capable of hydraulic setting by the addition of sufficient water thereto, such as, for example, Portland cement, hydraulic lime, blast furnace cement, or siderurgical cement, in an amount ranging between about 20.0 and about 65.0 percent by weight of the hydraulic mix;

2. anhydrous calcium chloride, in an amount ranging between about 0.2 and about 6.0 percent by weight of the mix; this compound acts to accelerate the initial setting of the cement;

3. a limestone marl or calcareous clay, containing between about 5 and about 50 percent by weight of clay; the

amount employed in the mix ranges between about 30.0

and about 76.8 percent by weight of the mix; and

\4. a slightly burnt and completely deacidified cement clinker in a proportion ranging between about 3.0 and 1 about 15.0 percent by weight of the mix.

instead of anhydrous calcium chloride, other hardening acbe used.

The clay contained in the limestone marl is advantageously of the montmorillonite type.

Instead of limestone marl, there can be employed a pure limestone, having a CaCO; content of about percent, to which a desired amount of montmorillonite-containing clay has been added.

The ingredient referred to as a slightly burnt and completely deacidified cement clinker is hereby defined more fully as a l cement or mortar material which has been subjected to a heat i treatment whereby a considerable transformation takes place. Depending upon the temperature applied, the material may deacidification (dissociation), sintering or even melting. Dead burned lime or magnesia are typically completely deacidified deposited by a mixed water and air spray upon the surface to 5 materials.

Z 1 attain partial or complete dehydration, partial or complete The hydraulic settable binding agents which are one ingredient of the composition of the invention are materials which have been burned at sintering temperatures.

The slightly burnt and completely deacidified cement clinker ingredient employed in the present invention is, in contrast thereto, a raw material of the type used for cement clinker production, in the form of a crude powder, having a CaCO content of about 78 percent, from which all the CO, is driven off by a heat treatment below sintering temperature. There is obtained thereby a practically dead burned lime, which however, contains ironand aluminum-silicate impurities. By means of the weak or slight burning, i.e., CO, removal, a chemical interchange between the burned lime and the ironand aluminum-silicate has not yet taken place, as would have been the case in the preparation of a true cement clinker. The slightly burnt and completely deacidified cement clinker refers to a material well known to those skilled in the art, and may be considered broadly as a type of cement.

For the purposes of the present invention, there may be employed any suitable type of slightly burnt and completely deacidified cement clinker. Advantageously the cement clinker will be one prepared in a so-called Lepol kiln. This ap paratus is fully described in US. Pat. No. 3,243,172 of Polysius G.m.b.H., and also at page 342 of the treatise "Anorganische Technologie II," by Winnacker-Weingaertner. It combines a drying or roasting grate and a rotary kiln. The material to be processed is fed in lumps to the grate, which may be either directly fired in the manner of a Dwight and Lloyd sintering machine, or which may be exposed to flue gases from the rotary kiln which are cycled to the grate. From the grate the dried or partly burnt material passes directly to the rotary kiln, in which burning to the desired extent takes place at elevated temperatures.

A cement clinker or cement as produced in a Lepol kiln is particularly advantageous in the cement or mortar mix of the present invention. It makes possible a very rapid setting and hardening of the mortar of the invention. The material as produced is in the form of a clinker, i.e., lumps, but can be further processed by fine grinding. The latter ground material can be more accurately characterized as a cement. It is hydratable and can be used directly in the mix of the invention by addition of water.

The slightly burnt, completely deacidified cement in the clinker form, having particles averaging 5 to 7 mm. in size, exhibits a bulk density of less than 1,000 g./liter.

The particle size of the previously mixed and then ground hydraulic cement or mortar mix of the invention is advantageously such that less than l0 percent is retained on a sieve having 140 mesh per inch.

The ground cement or mortar mix containing the four ingredients described above is applied by admixing therewith a quantity of water ranging between about 23 and about 40 percent by weight of the total quantity of mix and water, preferably 27.5 percent by weight. That is to say, a given hydraulic composition would comprise 77 percent by weight ofcement or mortar mix and 23 percent by weight ofwater.

In applying the mix of the invention, there may be employed a blower device of the conventional type, whereby the mix is blown dry and a sufficient quantity of water is added via a mixing nozzle to permit formation of a plastic paste which can then be sprayed at high pressure against the surface to be coated.

The cement clinker ingredient, e.g., Lepol kiln clinker, acts to prevent the wet mass, when sprayed against the surfaces, from flowing away by offsetting the slight liquefying effect of the calcium chloride. The cement clinker binds a part of the water added so that the mass stiffens immediately. The mass is then no longer flowable and because of the clay present, adheres to the surfaces to which applied.

The use of the mix prepared in accordance with the present invention has the great advantage that heavily worked sections in underground mining can operate with minimum interference by blowing the mixture over considerable distances through feed pipes. The mixture of the invention can be used to erect gastight, load bearing gallery bulkheads parallel to the wall faces by spraying the wet mixture against abutments such as sidewalls, posts and the like or on a waterproof cloth barrier, thus continuously constructing the accompanying barrier. The compressive strength achieved after 24 hours exceeds that of timber props. In contrast to known techniques, gastightness is also assured by the present invention.

The cavities between the supported cross-sectional area and the unsupported cross-sectional area of the galleries can be made gastight with the mix of the invention and sealing coatings of great strength and flexibility can be formed by spraying.

Furthermore, the mixture prepared in accordance with the present invention permits solid facings to be applied instead of brick facings at the beginning and end of sealing bulkheads by virtue of the fact that an adequate thickness of the mixture can be sprayed on partitions, and after the mix has hardened, the cavity can be rendered gastight by means of an aqueous slurry of stone dust and cement, thus eliminating expensive work involving high labor costs for the erection of sealing walls.

The mixture prepared in accordance with the invention is especially suitable for strengthening rock and for sealing seepage water, since the clay contained in the limestone marl can penetrate into the finest capillaries, producing great strength by reason of the clogging and swelling action of the clay.

DESCRIPTION OF THE PREFERRED EMBODIMENT I The preferred hydraulic cement or mortar mix of the invention has the composition:

Hydraulic cement burned to sintering 54 IL Limeltonc marl containing at least 5 wt. i; of clay 40 wt. 1: Anhydrous calcium chloride 1 wt. 90 Slightly burnt and completely de-ncidified Lepol kiln cement 5 wt.

Total l00 wt. I:

The Lepol kiln cement had a density of 600-800 g./liter.

A mortar mix was made with 72.5 parts by weight of the above composition and 27.5 parts by weight of water. The mortar was cast into rectangular prisms for purposes of tesu'ng compressive strength. The prisms had the dimensions l.575X1.575 inch on each side, height 6.30 inch. The hardened mass was tested at various temperatures at the end of periods varying from 6 hours to 28 days. The results are shown in the following table:

Temperature Tert Period 20' C. 30' C.

6 hours 15 kp./cm.' 20 kpJcm. 24 hours -100 kpjcl. l00-l25 kp.lcm. 3 days approx. I60 kpJcm. I60 kpJcm. 28 days I 300 kpJcm. Z 300 kpJcm,

The test results show that greater strengths are initially ob tained at higher temperatures.

Greater strengths are also obtained by increasing the quantity of cement clinker at the expense of the limestone marl. However, in such case, a limestone marl having a relatively low clay content should be used in order to achieve gastightness of sealing bulkheads and the like.

What is claimed is:

l. A hydraulic cement or mortar mix consisting essentially of a. from about 20 to about 65 percent by weight of a hydraulic binding agent capable of setting by addition of water thereto;

b. from about 30 to about 76.8 percent by weight of a limestone marl containing between about 5 and about 50 percent by weight of clay;

c. from about 0.2 to about 6.0 percent by weight of anhydrous calcium chloride; and

5. A hydraulic cement or mortar composition consisting essentially of 54 percent by weight of a sintered cement, 40 percent by weight of a limestone marl containing at least about 5 percent clay by weight, 1 percent by weight of anhydrous calcium chloride, and 5 percent by weight of a slightly burnt and completely deacidified cement.

6. The composition of claim 1 having added thereto sufficient water to effect hydraulic setting of the mix.

# 1. II t 

2. The composition of claim 1 in which the slightly burnt and completely deacidified cement is a cement clinker.
 3. The composition of claim 2 in which said cement clinker ranges in average particle size between about 5 and about 7 mm. and has a bulk density less than about 1,000 g./liter.
 4. The composition of claim 3 in which the bulk density ranges between about 600 and about 800 g./liter.
 5. A hydraulic cement or mortar composition consisting essentially of 54 percent by weight of a sintered cement, 40 percent by weight of a limestone marl containing at least about 5 percent clay by weight, 1 percent by weight of anhydrous calcium chloride, and 5 percent by weight of a slightly burnt and completely deacidified cement.
 6. The composition of claim 1 having added thereto sufficient water to effect hydraulic setting of the mix. 